#include<iostream> #include<vector> #include<queue> using namespace std; int main() { int h,w; cin >> h >> w; vector<vector<int>>num(h,vector<int>(w)); for(int i=0;i<h;i++)for(int j=0;j<w;j++)cin >> num[i][j]; priority_queue<vector<int>,vector<vector<int>>,greater<vector<int>>>prq1; priority_queue<vector<int>,vector<vector<int>>,greater<vector<int>>>prq2; vector<vector<int>>color(h,vector<int>(w,-1)); prq1.push({0,0,0}); prq2.push({0,h-1,w-1}); int cnt=1,ans=0; while(true){ ans++; if(cnt==1){ int a,b; while(true){ vector<int>hako=prq1.top(); prq1.pop(); a=hako[1]; b=hako[2]; if(color[a][b]==-1)break; } color[a][b]=1; if(a-1>=0){ if(color[a-1][b]==0)break; else if(color[a-1][b]==-1)prq1.push({num[a-1][b],a-1,b}); } if(b+1<w){ if(color[a][b+1]==0)break; else if(color[a][b+1]==-1)prq1.push({num[a][b+1],a,b+1}); } if(a+1<h){ if(color[a+1][b]==0)break; else if(color[a+1][b]==-1)prq1.push({num[a+1][b],a+1,b}); } if(b-1>=0){ if(color[a][b-1]==0)break; else if(color[a][b-1]==-1)prq1.push({num[a][b-1],a,b-1}); } cnt=0; } else{ int a,b; while(true){ vector<int>hako=prq2.top(); prq2.pop(); a=hako[1]; b=hako[2]; if(color[a][b]==-1)break; } color[a][b]=0; if(a-1>=0){ if(color[a-1][b]==1)break; else if(color[a-1][b]==-1)prq2.push({num[a-1][b],a-1,b}); } if(b+1<w){ if(color[a][b+1]==1)break; else if(color[a][b+1]==-1)prq2.push({num[a][b+1],a,b+1}); } if(a+1<h){ if(color[a+1][b]==1)break; else if(color[a+1][b]==-1)prq2.push({num[a+1][b],a+1,b}); } if(b-1>=0){ if(color[a][b-1]==1)break; else if(color[a][b-1]==-1)prq2.push({num[a][b-1],a,b-1}); } cnt=1; } } cout << ans-2 << endl; }